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    <title>Document</title>
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    <script>
        var years = prompt("请输入年份");
        if  ( (years%4) == 0 ) 
        {
            window.alert(years+"年是闰年！");
        } else 
        {
            window.alert(years+"年不是闰年！");
        }
    </script>
</body>
</html>